Peanuts (Arachis hypogaea L.) are grown worldwide in the tropic and temperate zones for seed oil and human foods such as peanut butter, roasted seed and confections. The final quality of edible peanuts is due principally to the chemical composition of the oil, protein and carbohydrate fractions of the seed. Since fatty acids make up the major portion of the weight of an oil molecule, the physical and chemical properties of the oil tend to be determined by the properties of the fatty acids which predominate in their makeup. Oils high in monounsaturates are desirable for both improved shelf life and potential health benefits.
Depending upon the intended oil use, different fatty acid compositions are desired. Peanut breeders face the dilemma of satisfying both the requirement of the manufacturer, which is stability of the processed product, and the demand from consumers for an increased polyunsaturated to saturated (P/S) ratio.
Oil stability and nutritional quality are both dependent on the relative proportions of the saturated and unsaturated fatty acids that constitute the oil. Moore, K. M. et al., J. Heredity 80 (3):252 (1989). Oxidative rancidity increases with increased levels of polyunsaturated fatty acids. Oxidation of the carbon double bonds of fatty acids produces acids, aldehydes, ketones, and other hydrocarbons that cause odors and flavors commonly associated with rancidity. St. Angelo, A. I. et. al., J. Am. Peanut Res. Educ. Assoc. 5: 128-133 (1973). The total amount of unsaturation, therefore, is inversely proportional to the keeping quality of the oil. The iodine value (IV) is a measure of oil chemical stability, with oils having higher IV being more unsaturated and chemically less stable. Low linoleic acid content ensures a product of high storage stability. Norden, A. J., WPI Accession No. 89-070645/10.
The American Heart Association and the American Health Foundation have recommended diet modifications to achieve lower serum cholesterol levels in the population. These diet modifications include reducing consumption of saturated fatty acids and thereby increasing the polyunsaturated to saturated (P/S) ratio in the diet. Technical Committee, Food Fats and Oils, 5th ed. (1982). Edible peanut oils with a higher percentage of unsaturated fatty acids are desired for these cardio-vascular health reasons. Mattson, F. H. et al., J. Lipid Research 26: 194-202 (1985).
High levels of the long-chain saturated fatty acids, arachidic and behenic are undesirable as they were suggested as being the responsible toxic element for enhancing atherosclerosis in rabbits fed diets utilizing peanut oil. Diets high in monounsaturates are able to lower serum cholesterol in a fashion similar to diets low in low fat. Grundy, S. M., New England J. Medicine 314(12): 745 (1986); Nutrition Foundation, Inc., Nutrition Review 30(3): 70-72 (1973). High levels of the monounsaturated oleic acid, which is present in olive oil, is as effective as the polyunsaturated linoleic acid in lowering the blood plasma cholesterol. Mattson, F. H., et al., J. Lipid Research 26: 194-202 (1985).
Although as many as 12 fatty acids have been reported in peanuts, only three are present in amounts exceeding 5%: palmitic, oleic and linoleic. Ahmed, E. M. et al. in Peanut Science and Technology (1982 H. E. Pattec, et al., ed.). These three fatty acids comprise about 90% of the fatty acid composition of the oil, with oleic and linoleic comprising about 80%. The remainder of the fatty acids comprise about 10%, each ranging in concentration from 0.02% to 2.59%.
Several factors affect the fatty acid composition of peanut oil: maturity, temperature, planting date, location, market grade, and peanut genotype. Moore, et al., supra; Cobb, W. Y. et al. in Peanuts-Culture and Uses (1973). Since 1970, studies on the genetic variability in the fatty acid composition of peanut genotypes have shown a range in the composition of the different acids. Norden, A. J., et al. Peanut Science 14:7-12 (1987).
Peanut genotypes are known with as low as 21% oleic and as high as 43% linoleic acid. One investigator sub-divided 100 peanut genotypes into three maturity groups and into four U.S. market-types. Bovi, M. L. A. Ph.D. Dissertation, University of Florida (1982). A large variation in oil quality was found within each market-type and/or maturity group. A peanut line with 79.91% oleic acid and 2% linoleic acid has been reported. Norden, et al., supra.
Fatty acid composition has been determined among seven U.S. runner-type peanut cultivars: `Florunner`, `Sunrunner`, `GK-7`, `Southern Runner`, `Sunbelt Runner`, and `Okrun`. Branch, W. D. et al., J. Am. Oil Chem. Soc. 67(9: 591-593 (1990). Variety `GK-7` is described in Plant Variety Protection certificate 82001413. Significant year and cultivar differences are found within these fatty acid profiles. Southern Runner had the greatest oleic to linoleic ratio of 2.3 and iodine values of 90.5. `Florunner` and `Sunrunner` were the highest in unsaturated and lowest in saturated and long-chain fatty acids. `Florunner` exhibits 51.7% oleic acid and 29.8% linoleic acid, while `GK-7` exhibits 49.6% oleic acid and 30.5% linoleic acid. `GK-7` and `Florunner` are the most widely cultivated peanut varieties in the United States.
Major genes for fatty acid composition have been reported in three oilseed crop species: sunflower (Helianthus annuus L.), soybean (Glycine max L. Merr.), and rapeseed (Brassica napis L.) Urie, A. L., Crop Sci. 25:986-989 (1985); Brunklaus-Jung E. et al., Plant Breeding 98:9-16 (1987); Erickson, E. A., et al., Crop Sci. 28: 644-646 (1988); Rennie, B. D. et al., Crop Sci. 28: 655-657 (1988).
Artificial irradiation has been used to induce changes in peanut lines to produce Spanish improved groundnut mutants that produce high oleic acid and low linoleic levels. More specifically, a parental Spanish improved line with 39% oleic acid was irradiated to make mutants that produce 61% oleic acid. Sharma, N. D., et al., Qual. Plant Foods Hum. Nutr. 35: 3-8 (1985).
The variation in oil quality among diverse peanut genotypes has been determined. Norden et al., supra. The range in the percent of the saturated fatty acids found among peanut genotypes in the Florida breeding program is not widely different from the ranges reported in other lines. Id. Oleic acid (18:1) levels in the oil of cultivated peanut (Arachis hypogaea L.) have been reported as 36% to 81.4% of the total fatty acid composition. Moore, K. M., et al., J. Heredity 30(3) :252-253 (1989); Knauft, D. A., et al., Peanut Science 20: 74-76 (1993) and Norden, et al., supra. A Spanish type high-oleic-acid peanut line, designated F435, exhibits 79.91% oleic acid and 2% linoleic acid. Moore, K. M. et al., supra. The peanut line F435 produces peanut seeds with an oleic acid content about 74-79.91% and linoleic acid content about 2-8%, based on total fatty acids, and an oleic acid:linoleic acid ratio of 9-42:1. French Patent Application 2617675 (See Tableau 1).
Initial genetic studies of the F435 peanut line showed that a single recessive gene controlled its fatty acid composition trait in two genetic backgrounds and a second recessive gene was necessary for expression in a third background. Moore, K. M. et al., supra. Further studies have shown that the high-oleic-acid trait in F435 is of monogenic inheritance in 12 parental backgrounds and digenic inheritance in one background. Knauft, D. A., et al., Peanut Sci. 20(2):74-76 (1993). This suggested that either one of the two recessive genes may be common in the Spanish variety peanut germplasm, and that crosses could be expected to segregate in simple monogenic ratios. Knauft, et al., supra. More recently, the number of genes controlling inheritance of the high oleic acid trait in F435 has been determined. Isleib, T. G., et al., Crop Science 36(3): 556-558 (1996). Segregation ratios of populations derived from crosses with NC-7, NC-9, NC-10C, and VA-C92R were consistent with a monogenic model and inconsistent with the digenic model. The activity of delta-12-desaturase, which catalyzes the conversion of oleate to linoleate, has also been shown to be greatly decreased in the F435 line. Ray, T. K. et al., Plant Sci. 91(1):15-21 (1993).
When the proportion of genes from F435 is reduced through backcrossing to less than 0.8%, fatty acid composition remains similar to the original F435 line. However, the concentration of oleic acid in F435 has never been shown to be greater than 79.91%. French Patent Application 2617675 (See Tableau 1); Brazil Patent Application 8803439; Japan Patent Application 1091720 and China Patent Application 1030691. One backcross made between F435 and F519.9, with F519.9 as the recurrent parent, resulted in a backcross having an oleic acid composition of 81.4=/-0.4%. Knauft, D. A., et al., Peanut Sci. 20(2):74-76 (1993). Also, the concentration of linoleic acid in F435 has never been shown to be less than 2.14%. French Patent Application 2617675 (See Tableau 1).
The high oleic acid trait of F435 has been transferred from the Spanish-type variety to one variety of runner-type to produce the commercially available runner-type peanut variety `SunOleic.RTM. 95R`. University of Florida Circular S 398 `SunOleic.RTM. 95R`. `SunOleic.RTM. 95R` does not yield as well as other runner-type varieties and exhibits appreciable preharvest pod-splitting. Id.
A need, therefore, remains for alternative sources of a high oleic acid characteristic that can be introgressed into diverse peanut backgrounds. In addition, a need exists for a high oleic acid characteristic peanut of the runner-type variety that has the additional characteristics of acceptable or high yield and negligible pod-splitting.